Try to avoid telling them what to do and influencing them too much. The best thing is usually to keep their options open by doing a broad range of subjects. But if they really don't enjoy something it's much better not to do it, as they probably won't do well and get a good result. It's great if they have teachers they can trust to talk it through with, especially if the teachers don't teach the subjects they are trying to choose between and can give impartial advice.

Unless your child has a very definite idea about what they want to do then I think the key thing is to play to your strengths. I have left it to my 2 dds to choose for themselves. They know the subjects they enjoy and the teachers they like working with.